Salts chromate

Silver Chromate. Silver chromate, Ag2Cr04, is prepared by treating silver nitrate with a solution of chromate salt or by heating a suspension of silver dichromate [7784-02-3]. 

Water-borne primers may or may not contain chromate-based corrosion inhibitors. The limited solubility of chromate salts in water makes them less than ideal for use in water-based primers, and much work has gone into developing alternatives [36], but the performance of recently developed water based primers using strontium chromate as the corrosion inhibitor is excellent, however, and appears equivalent to the solvent-borne analogues [37]. 

Ba2+] has dropped to 0.00055% of its initial value and therefore is considered to be completely precipitated, before SrCr04 begins to precipitate. The two ions are thus effectively separated as chromates. The best precipitating agent is a group 1 chromate salt. 

If excess base is added to this solution, it turns yellow, and yellow chromate salt may crystallize out. Thus, as mentioned above, in an aqueous solution of CrOs, there is an equilibrium between two Cr " species, namely, the chromate and dichromate ions ... 

The yellow solution of chromate salt on acidification turns orange due to formation of dichromate ion. Both the ions are in equilibrium, sensitive to pH change ... 

Chromium is used in the manufacture of stainless steel and other specialist steels, and non-ferrous alloys. Chromate salts are used as tanning agents, pigments, catalysts, corrosion inhibitors and in electroplating solutions. Although stainless steel is inert, the dissolution of chromium from this steel is likely to be the major source of chromium in food. 

Chromium in the +3 oxidation state is an essential trace element (see Section 10.3) required for glucose and lipid metabolism in mammals, and a deficiency of it gives symptoms of diabetes mellitus. However, chromium must also be discussed as a toxicant because of its toxicity in the +6 oxidation state, commonly called chromate. Exposure to chromium(VI) usually involves chromate salts, such as Na2Cr04. These salts tend to be water soluble and readily absorbed into the bloodstream through the lungs. The carcinogenicity of chromate has been demonstrated by studies of exposed workers. Exposure to atmospheric chromate may cause bronchogenic carcinoma with a latent period of 10 to 15 years. In the body, chromium(VI) is readily reduced to chromium(III), as shown in Reaction 10.4.3 however, the reverse reaction does not occur in the body. 

Chromium appeared to be better absorbed from the soil than from chromate salts, but less than 50% of the administered chromium could be accounted for in these studies, partly because not all tissues were examined for chromium content and excretion was not followed to completion (Witmer et al. 1989,... 

Although skin contact with chromate salts may cause rashes, untreated ulcers or sores (also called chrome holes) on the skin can be a major problem because they can deeply penetrate the skin with prolonged exposure. For example, in an early case of a tannery worker, the penetration extended into the joint, necessitating amputation of the finger (Da Costa et al. 1916). However, chrome sores heal if exposure is discontinued, leaving a scar. Chrome sores are more often associated with occupational exposure to chromium(VI) compounds. Although chrome sores are more likely associated with direct dermal contact with solutions of chromates, exposure of the skin to airborne fumes and mists of... 

Gad SC, Powers WJ, Dunn BJ, et al. 1986. Acute toxicity of four chromate salts. In Serrone DM, ed. Chromium symposium 1986 An update. Pittsburgh, PA. Industrial Health Foundation inc., 43-58. 

This pigment, also called zinc yellow, is produced by reacting an aqueous slurry of zinc oxide or hydroxide with dissolved chromate ions, followed by neutralization, or by precipitation of dissolved zinc salts with dissolved chromate salts, followed by washing, filtration, drying, and milling processes [5.56]. Previously zinc yellow used to hold a major share of the anticorrosive pigment market... 

SAFETY PROFILE Chromate salts are suspected human carcinogens producing tumors of the lungs, nasal cavity, and paranasal sinus. Chromic acid and its salts have a corrosive action on the skin and mucous membranes. The lesions are confined to the exposed parts, affecting chiefly the skin of the hands and forearms and the mucous membranes of the nasal septum. The characteristic lesion is a deep, penetrating ulcer, which, for the most part, does not tend to suppurate, and which is slow in healing. Small ulcers, about the size of a matchhead, may be found, chiefly around the base of the nails, on the... 

Chemical Abstracts Service Registry Numbers CAS 5188-42-1 (chromate salt) CAS 6272-66-8 (dinitrate salt)... 

From such solutions orange dichromate salts can be crystallized after adding a stoichiometric amount of base. Addition of excess base produces yellow solutions from which only yellow chromate salts can be obtained. The two anions exist in solution in a pH-dependent equilibrium. 

At about the same time, chrome-lignin grouts (lignosulfonate solutions catalyzed with chromate salts) were proposed and developed for field use. 

Alumina was synthesized from precipitated gel of aluminium hydroxide which was extruded to cylindrical pellets and activated under controlled conditions to yield high surface area. Chromia was loaded on alumina by soaking alumina in soluble chromates salts and activated in muffle furnace at about 600 C (4 to 10)... 

Potassium chromate 4 186 K2 4 Chromate of potassa monochromate of potassa neutral chromate of potassa potasJtc chromate salt of chrome yellow chromate of potassa. 

Indicators Reacting with the Titrant. There are several examples of an indicator forming a colored compound with a titrant. The Mohr method for determining chloride serves as an example. The chloride is titrated with standard silver nitrate solution. A soluble chromate salt is added as the indicator. This produces a yellow solution. When the precipitation of the chloride is complete, the first excess of Ag reacts with the indicator to precipitate red silver chromate ... 

Caution, Chromic acid or chromate salts constitute industrial hazards. Irritant effects on the skin and respiratory passages lead to ulceration. Oral ingestion may lead to severe irritation of the gastrointestinal tract, circulatory shock and renal damage. Chronuum(lll) compounds show little or no toxicity. This substance and certain chromium compounds have been listed as known carcinogens Fourth... 

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